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DNA Shifts Timeline for Mammoths’ Exit

Thousands of years ago in northwestern North America, large animal species, among them the woolly mammoth and the horse, became extinct. Among the proposed explanations for this is one known as the blitzkrieg hypothesis — that humans entering the region rapidly wiped the animals out through overhunting.

The validity of that explanation, and others, depends in parts on the timing of the extinctions. How many thousands of years ago did the animals disappear?

Until now, the answer to that question has been 13,000 to 15,000 years ago. But those dates come from the youngest reliably dated fossils that have been found, and who is to say there aren’t even younger fossils out there?

A new study has come up with a far different answer, using a far different technique.

Rather than dating actual fossils, the researchers analyzed DNA found in permanently frozen sediments at a site on the Yukon River in central Alaska. As they report in The Proceedings of the National Academy of Sciences, they found evidence that mammoths and horses were still around at least until 10,500 years ago, long after humans arrived.